The Second International Lymphokine Workship decided to adopt a unified name, interleukin-1 (IL-1), for the physiologically active substances which had been referred to as lymphocyte activating factor (LAF), mitogenic protein, helper peak-1, T-cell replacing factor III (TRF-III), T-cell replacing factor M.phi. (TRFM), B-cell activating factor, B-cell differentiation factor, etc. (Cellular Immunol., 48, 433-436 (1979)). This decision is based on the reason that these physiologically active substances can not be distinguished from one another as different substances but are expressed variously merely with reference to physiological activities as interpreted from different angles.
Further it is reported that IL-1 activates T lymphocytes and B lymphocytes, has activity to promote production of interleukin-2 and antibodies, acts on liver tissues to promote protein synthesis and possesses activity to promote production of prostaglandins (see Reviews of Infectious Disease, Vol. 6, No. 1, 51-59 (1984), New England J. of Med., 311, 1413 (1984), etc.).
Whereas IL-1 itself still remains to be clarified as a substance, it is only recently that reports are made on the presence of genes coding for polypeptides having LAF activity or precursor thereof (Proc. Natl. Acad. Sci., Vol. 81, 7907-7911 (1984), Nature, Vol. 315, (1985), Nucleic Acid Research, Vol. 13 (16), 5869 (1985)).
According to the report, a culture supernatant obtained by gene recombination techniques was found to have LAF activity, and based on this finding, it is speculated that the polypeptide represented by the following formula (A) is a polypeptide having LAF activity and is termed "IL-1.alpha.." ##STR1##
However, no reports have been made to the effect that the above active substance, as well as the physiologically active substance which is reportedly known as the so-called IL-1, is prepared and isolated as a homogeneous substance, nor has there been any report on the physiologal activity of such a homogeneous substance.
We conducted intensive research on IL-1.alpha. as a homogeneous substance and already established a technique for preparing this substance and clarified the characteristics, physiological activity, etc. thereof. Based on the results of the research, we also confirmed that the polypeptide of the foregoing formula (A) has LAF activity.
Nevertheless, we have found the surprising fact that the polypeptide, although corresponding to a gene of the living body as reported, is unstable as a substance.